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Solid state nuclear magnetic resonance studies of high-performance battery electrode materials

Final Report Summary - NMRHIPBAT (Solid state nuclear magnetic resonance studies of high-performance battery electrode materials)

Metal fluorides/oxides (MFx/MxOy) are promising electrodes for lithium-ion batteries that operate through conversion reactions. These reactions are associated with much higher energy densities than intercalation reactions, on which the commercial rechargeable lithium ion batteries are based. The fluorides/oxides also exhibit additional reversible capacity beyond their theoretical capacity through mechanism that was poorly understood, in part owing to the difficulty in characterizing structure at the nanoscale, particularly at buried interfaces. This project employs high-resolution multinuclear/multidimensional solid-state NMR techniques, together with theoretical calculations showing that a major contribution to the extra capacity in this system is due to the generation of LiOH and its subsequent reversible reaction with Li to form Li2O and LiH. This study has established a protocol for studying the structure and spatial proximities of nanostructures formed in this system, including amorphous solid electrolyte interphase that grows on all battery electrodes.

Socio-economic impacts

1. Battery degradation. Degradation is one of the major issues faced by the leading energy storage technologies. Degradation affects the lifetime of energy storage devices and energy conversion efficiency, e.g. in rechargeable batteries, thus adding to the cost and also causing safety concerns. Most of these degradation reactions occur at electrode-electrolyte interfaces. In order to mitigate this problem, a fundamental understanding of the reaction mechanism at these interfaces is critical. The amorphous nature and complexity of the interfacial structure makes the characterization quite challenging. The protocol developed in this study lends a suitable tool to probe the structure, chemical composition, and the mechanism for these degradation reactions. This characterization method will be attractive to energy-storage industry, which are currently seeking effective ways to minimize the degradation issue by adding various expensive additives into the device without comprehending what kind of reactions occurring and how to optimize the structure of the additive to enhance their efficiency. Since Europe heavily relies on an efficient transport system, which shall be supported by renewable energy sources combined with energy storage systems in the near future. Cost reduction for harvesting and storing energy will be one of the most relevant issues to address.
2. Interface science. This study demonstrates the advantage of solid-state NMR in studying “buried” disordered interfaces. Interfaces exist in all composite materials relevant to energy (catalysis, solar cells, fuel cells), health, materials, and environments, etc. NMR can be used as a useful tool for research of various areas that benefit the society in the short and long run.